This invention relates to power-driven shovels and, more particularly, is concerned with a conventional loader type of backhoe mechanism mounted on a tractor or similar vehicle to present a center of gravity more closely adjacent the tractor, thereby improving the balance and handling during loading and transport.
In the conventional prior art arrangements, the transport position is characterized by a generally vertically and slightly rearwardly extending boom carrying a folded dipper assembly positioned as close as possible to the boom to hold the main center of gravity for the backhoe as near as possible to the rear of the mounting vehicle. However, the main center of gravity is still so far to the rear of the vehicle that mechanical balance relationships are insufficiently stable and handling is unduly difficult, even during normal use as a loader. On conventional backhoes, proper weight distribution is accomplished by placing counterweights on the front of the tractor. Counterweights have the disadvantage of increasing total weight of the vehicle, and do not improve stability due to the inertial moments caused by the length of conventional backhoes.
Commonly assigned U.S. Pat. No. 3,376,984 to Long et al. solves these problems by providing a backhoe arrangement which is arranged to accommodate an overcenter movement of the boom cylinder assembly when the boom is swung to the transport position. In the transport position, the backhoe has a generally vertically and slightly forwardly extending boom held locked in position by the boom cylinder assembly which has gone overcenter. The ability of the boom to assume a more forwardly inclined relationship effects an improvement in the position of the center of gravity to provide better balance and handling and to limit the backhoe tail swing required in close quarter operations.
However, the Long arrangement, and the other prior art arrangements, comprise a single unitary boom flanked on both sides by boom cylinder assemblies, and have the disadvantage of poor visibility of the bucket by the operator.